There is known a method of ultrasonic inspection of articles, including the steps of selecting parallel directions of transverse ultrasonic oscillations radiated into an article and of transverse oscillations mirror-reflected by the reflecting surface of a flaw of a weld of the article and by the surface of the article, these directions belonging to the planes of polarization of the radiated and registered transverse oscillations, coinciding with one another and with the plane of incidence of these oscillations upon the reflecting surface of the flaw of the weld of the article, and intermittently radiating into the article transverse ultrasonic oscillations and registering transverse oscillations reflected by the reflecting surface of the flaw and by the surface of the article, for evaluating the geometrical parameters of the flaw (SU, A, 461361).
According to this method, the transverse oscillations incident upon the reflecting surface of the flaw are vertically polarized with respect to this surface. These oscillations are transformed into other kinds of oscillations, e.g. longitudinal oscillations, when their angle of incidence upon the reflecting surface of the flaw is either close to or short of the third critical angle. In this case the reflection factor of the transverse oscillations by the reflecting surface of the flaw sharply drops, and at the same time the interference caused by other kinds of ultrasonic oscillations is reinforced. Consequently, both the sensitivity of ultrasonic inspection in accordance with this known method and its immunity to interference are relatively low, which can be vividly seen in its implementation for inspection of welds of articles of relatively small thickness (below 30 mm).
Besides the low sensitivity and immunity to interference of this known method, it is further characterized by the necessity, in its implementation for inspection of welds of articles thinner than 30 mm, of arranging the piezoelectric transducers employed for radiating and registering the ultrasonic oscillations very close to one another on the surface of the article, which is not always possible on account of the own geometric dimensions of the piezoelectric transducers themselves.
There is further known a method of ultrasonic inspection of welds of articles, including the steps of specifying the direction of radiating transverse ultrasonic oscillations into an article, the plane of polarization of transverse ultrasonic oscillations radiated into a weld of the article, the plane of their incidence upon the reflecting surface of a flaw of the weld of the article, the direction of mirror reflection of these oscillations by the reflecting surface of the flaw of the weld of the article and the plane of polarization of transverse ultrasonic oscillations registered upon their mirror reflection by the reflecting surface of the flaw of the weld, and intermittently radiating transverse ultrasonic oscillations into the article and registering the transverse ultrasonic oscillations reflected by the reflecting surface of the weld of the article, for evaluating the geometric parameters of the flaw (SU, A, 855487).
According to this method, the transverse ultrasonic oscillations radiated into the article contain components which are both vertically and horizontally polarized with respect to the reflecting surface of the flaw of the weld of the article. This is attained owing to the respective directions of radiating transverse ultrasonic oscillations and their mirror reflection being symmetrical with respect to a plane perpendicular to the longitudinal axis of the weld and including the flaw.
However, the ratio of the amplitudes of these respective components is such that the amplitude of the vertically polarized component tends to be significantly greater. This results in a reduced amplitude of transverse oscillations reflected by the flaw, the growing amplitude of transformed longitudinal oscillations and, consequently, in impaired sensitivity and immunity to interference of the ultrasonic inspection procedure, i.e. to adversely affected credibility of the outcome of the inspection.
Furthermore, the last-described known method would not be implemented for ultrasonic inspection of pipes of diameters in excess of 100 mm and of flat articles, since in such cases it would be impossible to maintain the directions of radiation and registration of ultrasonic oscillations, required by the method.